Apparatus for producing radiographs of curved planes in an object

ABSTRACT

An x-ray source and a film cassette are mounted on opposite ends of an arm that swings in a horizontal plane about a vertical axis so that the cassette and source jointly orbit a patient of whom a panoramic dental radiograph is desired. On an overhead base is a first carriage which is on a track that constrains the carriage to move back and forth in a single line along one coordinate axis. A second carriage is carried on the first carriage and is on a track that constrains it to move only at a right angle to the first carriage along the other coordinate axis. The second carriage has a bearing that supports the horizontal arm. A driving arm is engaged with the second carriage and drives both carriages so that their resultant motion is a semi-ellipse that approximates the shape of the dental arch. The vertical rotational axis of the arm is always on the semi-ellipse or other desired curve. Means are provided for translating the cassette and for keeping the arm perpendicular to the curve at all times.

United States Patent [1 1 Wright [451 July 3, 1973 APPARATUS FOR PRODUCING RADIOGRAPHS OF CURVED PLANES IN AN OBJECT [75] inventor: William E. Wright, Hales Corners,

Wis.

[73] Assignee: General Electric Company,

Milwaukee, Wis.

[22] Filed: Nov. 6, 1968 [21] Appl. No.: 773,807

2,798,958 7/l957 Hudson et al... 250/61.5

2,976,417 3/l961 Freeman 250/65 3,536,913 10/1970 Huchel 250/6l.5

Primary Examiner-William F. Lindquist Attorney.lames E, Espe, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. Forman [57] ABSTRACT An x-ray source and a film cassette are mounted on opposite ends of an arm that swings in a horizontal plane about a vertical axis so that the cassette and source jointly orbit a patient of whom a panoramic dental radiograph is desired. On an overhead base is a first carriage which is on a track that constrains the carriage to move back and forth in a single line along one coordinate axis. A second carriage is carried on the first carriage and is on a track that constrains it to move only at a right angle to the first carriage along the other coordinate axis. The second carriage has a bearing that supports the horizontal arm. A driving arm is engaged with the second carriage and drives both carriages so that their resultant motion is a semi-ellipse that approximates the shape of the dental arch, The vertical rotational axis of the arm is always on the semi-ellipse or other desired curve. Means are provided for translating the cassette and for keeping the arm perpendicular to the curve at all times.

6 Claims, 9 Drawing Figures Patented July 3; 1973 I 5 Sheets-Sheet l Patented July 3, 1973 5 Shaets-$heet I Patented July 3, 1973 5 Sheets-Sheet 3 Patented July 3, 1973 3,743,832

5 Sheets-Sheet 4 Patented July 3, 1973 3,743,832

5 Sheets-Sheet 5 APPARATUS FOR PRODUCING RADIOGRAPHS OF CURVED PLANES IN AN OBJECT BACKGROUND OF THE INVENTION Panoramic x-ray units are adapted to radiograph the upper and lower teeth and jaw structure as a continuous process on an extra-oral film. An arm that rotates in a horizontal plane, supports at one end an x-ray tube that projects a beam at a slightly upward fixed angle through the subjects face. A film cassette carrier is mounted at the opposite end of the arm for jointly orbiting about the subject with the x-ray tube so that a progressive x-ray image of the teeth is projected and recorded on the film. The film cassette is behind a slit in an x-ray impervious face of the carrier and the cassette is translated or rotated at an appropriate speed in the cassette carrier. The process is comparable to plane surface tomography where the rotational axis of the x-ray tube and cassette arm lies essentially parallel and in coincidence with the plane that is recorded. Thus, the plane of interest remains equidistant from the film and x-ray tube focal spot so a sharp image of this plane is formed. Other planes undergo relative motion and are blurred out on the radiograph.

When radiographing a curved plane within the subject with prior types of apparatus, the distance between the curved layer of interest and the film varies as the x-ray tube swings in a circle and the x-ray beam does not remain normal to the plane at all times. This causes SUMMARY OF THE INVENTION A primary object of the present invention is to overcome the above-noted defects with a curved plane radiography apparatus that is characterized by the vertical axis of the tube arm being translated so that it is always coincident with the curved plane being radiographed. This permits taking a complete panoramic dental radiograph without interruption and without the need for shifting the subject or the equipment.

A further object is to provide a dental radiography unit with a mechanism for translating said vertical axis through a semiellipse or a little more, to closely approximate the contour of the dental arch extending from one mandibular joint to the other and to rotate the horizontal tube arm in such manner as to maintain it in perpendicularity at all times with a line that is tangent to the curved plane.

Another object is to provide means for adjusting the size of the elliptical pattern to accommodate subjects with different sized dental arches.

Still another object of the invention is to vary synchronously the rotational speed of the x-ray tube arm and the translational rate of the film cassette to compensate for the dental arch varying in curvature between the anterior and posterior regions.

How the foregoing and other more specific objects are achieved will appear in the ensuing description of preferred embodiments of the invention taken in conjunction with thedrawings.

DESCRIPTION OF THE DRAWINGS the unit shown in FIG. 1, this view being for facilitating a general description of how the invention operates;

FIG. 3 is a partial top view, with parts removed, of the part of the mechanism which is for translating the axis of the tube arm over an ellipse that coincides with the dental arch;

FIG. 4 is a partial vertical sectional view taken on the line 4-4 of FIG. 6;

FIG. 5 is a front elevational sectional view, with parts broken away, taken on the line 5-5 of FIG. 3;

FIG. 6 is a top view showing some of the mechanism for generating the dental arch ellipse together with some of the mechanism for rotating the arm;

FIG. 7 is a vertical sectional view taken on the line 7-7 through the ellipse generating mechanism shown in FIG. 6',

FIG. 8 is a vertical sectional view taken on the line 8-8 at the left-end of the ellipse generating mechanism shown in its top view in FIG. 6; and,

FIG. 9 is a horizontal section taken through the eassette holder and surrounding radiation shield together with the belt and sprockets for rotating the cassette holder.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a subject 1 positioned for taking a panoramic dental radiograph of the upper and lower teeth and the jaw structures. The subject sits on a chair 2 with his head positioned between an x-ray tube casing 3 and a film cassette holder 4. A beam of x-rays is projected from the focal spot of an x-ray tube within casing 3 through an exit slit 5 for collimating the beam so it has a narrow horizontal dimension and a long vertical dimension. The beam penetrates the subject and causes an x-ray image to be formed on a film within cassette carrier 4. The x-ray image projects through a narrow slit 6 in the front of carrier 4, see FIG. 2.

In FIG. 1, x-ray tube casing 3 is carried on one end of an arm 7 at the other end of which is the cassette carrier 4. The arm 7 is adapted to rotate on a vertical axis in a horizontal plane so that the x-ray tube casing 3 and cassette carrier 4 orbit the subject 1 in the course making a panoramic dental radiograph. The axis of rotation of arm 7 coincides with the center of a cylindrical hollow sleeve 8 which extends into a housing 9 that is over the head of the subject. Housing 9 contains mechanism, to be described below, for rotating arm 7 about its vertical axis, for translating the vertical axis so it follows over the dental arch of the subject, for generating the ellipse which coincides with the dental arch and for rotating the film cassette while making a radiograph.

A chin rest 10 is used for locating and steadying the subject while an x-ray exposure is underway. The chin rest is supported on a swinging arm 11 which can be swung upwardly on a hinge joint 12 to get the arm out of the way when setting up the subject. The chin rest can also be mounted on chair 2 if desired.

Light beam sources may also be provided for projecting beams on the front and side of the patientface so that all reference points on the subjects head will be at the proper location for initiating a radiograph. The light beam sources are not shown because they are conventional and can be readily devised by a skilled designer.

The angular position of tube arm 7 in FIG. 1 coincides with its position when a panoramic dental radiograph is about half completed with the apparatus. At this time, the x-ray beam is being projected out of slit through the back of the patients head toward cassette carrier 4. FIG. 2 shows the arrangement of these parts when the subject is ready for initiating a radiograph. The vertical axis of the tube arm projects down through the subjects left mandibular joint 13. This joint is the first to be imaged on the cassette in carrier 4. Rotation of tube casing 3 is then initiated in a clockwise direction as shown, at which time tube casing 3 and carrier 4 orbit the subject. Carrier 4 and the eassette within it maintain an essentially constant distance between the plane in the subjects dental arch being radiographed and the plane of the film. At the end of the radiograph, tube casing 3 and carrier 4 have rotated in excess of 180 and, in one embodiment, about 210.

When taking a radiograph as just described in reference to FIG. 2, the vertical axis of the tube arm 7 is always on the dental arch or projected vertically through it. This enables maintaining a constant x-ray focal spotobject-film distance relationship and permits maintaining perpendicularity between the x-ray beam and the plane being radiographed. Thus, geometrical distortion of the teeth and jaw structures on the film is minimized. There will be a subsequent discussion on the matter of varying the rotational velocity of tube arm 7 in order to account for density differences that exist through various vertical planes through the subject and for the fact that the x-ray beam must be sweeping fastest where the dental arch is changing curvature most rapidly, such as at the front, in order to maintain perpendicularity between the x-ray beam and the curved plane being radiographed.

In FIG. 1, housing 9 and the mechanism which it contains extends horizontally from a stationary column 14. Housing 9 is adapted to be moved up and down on column 14 to adjust the level of the x-ray tube casing and cassette carrier 4 to the height of the subject 1. The vertical adjusting mechanism is not shown because it is conventional and may be readily devised.

The mechanism for moving the vertical axis of rotation of tube arm 7 in an ellipse so that the vertical axis projects down through the dental arch and always coincides with it will now be discussed primarily in reference to FIGS. 3, 4, 6 and 7.

In FIG. 3, the bottom of housing 9 which is over the patients head is marked with the reference numeral 15. This bottom or base plate supports a first carriage,

16 which runs on pairs of upper and lower rollers 17 I and 18 which are on stud shafts that are fastened to the carriage 16. At the far left end in FIG. 3, but not shown because the region is broken away, carriage 16 is provided with a similar set of rollers except that the lower rollers corresponding with 17 have a V-groove which enables them to run on a round track, not shown, that extends from the front to the rear and is mounted on base plate 15. By this means, carriage 16 is constrained to move only forward and backward as shown in FIG. 3. Within outer carriage 16, is a second carriage 19 which is provided at its rear with sets of upper rollers 20 and lower rollers 21. These may be mounted for rotation on studs extending from the back of the carriage 19. In the front of carriage 19 is a pair of lower rollers 22 which have V-grooves and a pair of upper rollers 23. There are two sets of such rollers at the front of carriage 19. The rollers 22 with the peripheral V-groove run on a track 24 which is fastened at its ends to the interior and bottom of outer carriage 16. Track 24 may be a round rod, for instance. It is easy to see that if a force is applied perpendicularly to the front or the rear of the second or inner carriage 19 that the outer carriage 16 will yield backwards or forward, respectively, by reason of the force being transmitted to the outer carriage. The force is transmitted by way of the V- groove in rollers 22 engaging with rail 24 which is fixed to the outer carriage 16. If the inner carriage 19 is subjected to a force which tends to urge it to the left or right, it will merely roll to the left or right along rail 24 and the outer carriage 16 will not move because it is constrained to move only forward and backwards. Thus, if anything projecting from inner carriage 19 is subjected to a force which would tend to move it in an ellipse or other pattern, the outer carriage 16 will move in response to the backward and forward components of motion and the inner carriage 19 will move in response to the sidewise components of motion. Hence, any point on the inner carriage 19 will trace an ellipse or whatever curve has been generated and applied to it.

As can be seen in FIG. 4, the arm 7 which supports the x-ray tube casing 3 and the cassette carriage 4 is supported from the inner carriage l9. Fastened to the top of arm 7 with bolts 25 is a hollow shaft 26. Shaft 26 has a circumferential shoulder at its top which bears on a thrust bearing 27. There is also a lower thrust bearing 28. Both thrust bearings 27 and 28 are set in suitable annular recesses at opposite ends of a cylindrical spacer 29 which is fastened to inner carriage 19. Thus, arm 7 is adapted to swing in a horizontal plane on a vertical axis coinciding with the center of hollow shaft 26 which is in turn journalled for rotation on inner carriage 19. Arm 7 also translates with inner carriage l9 and with outer carriage 16. Hollow shaft 26 projects through an opening 30 in the bottom of outer carriage 16. There is, of course, another opening in bottom plate or base 15, see FIG. 3, so that hollow shaft 26 may move in an elliptical path without interference.

Shaft 26 has a ring gear 31 pressed on its upper end so that it may be driven rotationally. Rotational driving force for gear 31 comes from a speed reducer 32 which is mounted on inner carriage 19 through the agency of a bracket, not shown, and a plate 33. Speed reducer 32 has a shaft 34 extending from it. This shaft carries a gear 35. The latter engages with another gear 36 which is on a shaft 37 that is journalled at 38 in plate 33. The upper end of shaft 37 is journalled at 40 in another plate 39. Plate 39 is supported on posts 41 from lower plate 33, only one post being shown in FIG. 4. Shaft 37, besides carrying gear 36, has at its upper end a gear 42. The latter gear meshes with a gear 43. Gear 43 is carried on a shaft 44 which is journalled in upper plate 39 and lower plate 40, as shown, and has at its lower end a pinion 45 fixed on it. Pinion 45 meshes with ring gear 31 on vertical hollow shaft 26. Thus, it is seen that when speed reducer shaft 34 turns, the hollow shaft 26, supporting tube arm 7, also turns. 1

Gears 42 and 43 determine the rate and amount of rotation of hollow shaft 26. As shown, gear 42 has 65 teeth and gear 43 has 55 teeth. With this gear ratio, hol low shaft 26 and, of course, tube arm 7 are adapted to rotate approximately 210. To adapt for 180 of arm rotation, gears 42 and 43 may have equal numbers of teeth. In one embodiment of the invention, not shown, elliptical gears are substituted for gears 42 and 43 in which case the tube arm will rotate at a variable speed as the vertical axis of the hollow shaft 26 is traversed over the dental arch. Use of the elliptical gears assures perpendicularity between the tube arm and dental arch at all times.

Now that the mechanism has been described for rotating hollow shaft 26 and tube arm 7, attention will be directed to the manner in which an ellipse simulating the dental arch is produced and to the manner in which the vertical axis of hollow shaft 26 is traversed over the dental arch of the subject. As explained earlier, this involves applying a force to inner carriage 19 so that a point on it can yield with outer carriage 16 to trace an ellipse or other configuration.

In FIG. 3, one may see that an electric motor 50 drives speed reducer 32 from which power is taken to rotate hollow shaft 26 as described and to operate the ellipse generating mechanism which is generally designated by the reference numeral 51, see FIG. 6. Reverting to FIG. 4, one may see that gear 35 which is on the speed reducer shaft engages with a gear 36 which is on shaft 37. Shaft 37 also carries a sprocket 52 which drives a chain 53. Chain 53 extends back to the ellipse generating mechanism 51 as can be seen particularly well in FIG. 6. t

The ellipse generating mechanism used here is similar to a trammel which is characterized by two bars perpendicular to each other and a cross-bar or arm adapted to pivot and slide on each of them. When the cross-bar is slid down one of the perpendicular bars, it must yield along the other, thus causing an ellipse to be generated by any point on the cross-bar. The distance between the sliding pivots establishes the major and minor axes of the ellipse.

Now considering FIGS. 6 and 7, one may see that there is a lower bar 54 which is mounted on suitable posts such as 55 and fastened to base plate 15. There is another bar 56 which is perpendicular to bar 54. Bar 56 is in a different plane than bar 54and is attached to a supporting member 57 which is bent downwardly to form legs as can be seen in FIG. 7. The arm of the trammel in this case comprises an upper flat member 58A and a lower flat member 588 which members are joined through the agency of a vertical flat member 58C. Thus, members 58A and 58B and their joining member 58C form a U-shaped arm assembly.

Member 58A is adapted to slide and pivot with respect to fixed bar 56. For this purpose there is provided a guide member comprising upper and lower plates 61 and 62, respectively. There are three shafts having boltheads 63 spanning the distance between upper and lower plates 61 and 62. Also provided are guide rollers such as 64A and 648 to allow the whole assembly to slide along bar 56 easily. This connection between this assembly and member 58A of the arm is a pivot shaft 66 which is journalled for rotation in lower plate 62. Flat member 58A of the arm is slotted as indicated at the reference numeral 59 so shaft 66 can pass through member 58A.

Shaft 66 terminates in a unitary metal block 67 through which there is a lead screw 68. The lead screw is journalled at 69 in a block 70 which is attached to member 58A and a shaft 80. Block 67 is threaded where lead screw passes through it and it should be evident that turnung lead screw 68 will cause block 67 and shaft 66 to move to the right or left in slot 59, as seen in FIG. 7. By this means, the center of rotation of the pivot shaft 66 may be shifted and adjusted with respect to arm member 58A. The purpose of this is to permit setting the size of the minor axis of the ellipse which corresponds with the approximate distance between mandibular joints.

Lower member 58B is similarly pivotally connected with stationary bar 54. Again the guiding and pivot assembly comprises upper and lower plates 71 and 72 which are joined by suitable shafts and carry rollers such as 73A and 738 on each side of bar 54 to permit the assembly to slide or roll along bar 54. Extending from plate 71 is a pivot shaft 74 which passes through a slot 75 in lower flat member 588. Shaft 74 also terminates in a block 76 which is threaded for a lead screw 77. Lead screw 77 is journalled at 78 in a block 79 which is fixed on a shaft 80. Turning lead screw 77 will adjust the pivot point and permit setting the size of the major axis of the ellipse which corresponds essentially with the distance from the subjects incisors back to a line running thru each mandibular joint.

Block 76 carries a tab 81 which is clamped to a belt 82. The latter runs on idler pulleys 82A and takes a turn around a pulley 83. Pulley 83 is on a potentiometer shaft 84. By electric circuitry, not shown, the potentiometer driven by shaft 84, delivers a signal to an external indicating device which is calibrated to indicate the size of the ellipse resulting from setting the pivot point for the arm which controls the major axis of the ellipse. In this case, the indicated signal provides complete information on the dental arch size setting because a fixed ratio has been chosen for the major and minor axes of the ellipse. In other words, it is assumed in this design that for most patients, the major axis of the dental arch ellipse is substantially equal to twice the length of the minor axis.

Tab 81 also operates limit switches 85 and 86 to turn off the ellipse adjusting driving motor 87 when the limit of adjustment has been reached.

Motor 87 which is operated to turn lead screws 68 and 77 simultaneously for setting the size of the generated ellipse is seen best in FIG. 6. From this motor projects a shaft 88 on which there is a gear 89 that meshes with a gear 90 as can be best seen in FIG. 7. Lead screw 68 has a gear 91 fixed on its end. The lower lead screw 77 has a gear 92 fixed on its end. Gear 91 has twice as many teeth as does gear 92. When these gears are driven by the common driving gear 90,they effect a simultaneous adjustment of the size of both ellipse axes.

An end view of the gear train driving upper lead screw 68 and lower lead screw 77 is shown in FIG. 8.

trace is transmitted back to inner carriage 19 through a force transmitting member 97, see FIG. 6. This member is fastened by means of bolts 119 to the heavy plate 33 which is attached to inner carriage 19. The end of the force transmitting member 97, which is most remote from the carriage 19, is bifurcated. Upper and lower sections 98 and 99 taken through the bifurcated end may be seen particularly well in FIG. 7. These sections are provided with bearings such as 100 which evidences that they are free to turn on shaft 80 when the shaft is executing an ellipse. This concludes the discussion of the ellipse generating mechanism and the means by which the elliptical trace so generated is transmitted to the carriages for causing them to execute the same elliptical trace jointly. The elliptical trace is also followed by the vertical axis of hollow shaft 26 which supports and rotates tube arm 7. This vertical axis passes through and follows the dental arch of the subject.

While the tube arm 7 is being swung and its rotational axis is being translated in an ellipse to take a panoramic dental radiograph of the subject, it is, of course, necessary to present unexposed film in the path of the x-ray beam as the radiograph progresses. The film carrier is designated generally by the reference numeral 4 in FIG. 1 and is shown more particularly in cross-section in FIG. 9. The outside of the film carrier is provided with a stationary radiation shield 101 in which there is a slit 6 for admitting the x-ray image to a film cassette 102. The film cassette 102 may be any flexible or rigid type which allows it to be wrapped around a circular cassette drum 103 which is adapted to be rotated to present new film in front of slit 6 as the radiograph progresses. Generally, the films are by 14 inches and the circumference of drum 103 must be sized accordingly. The film cassette supporting drum 103 must rotate synchronously with arm 7 as the latter is swung during making a radiograph. The rate at which the film drum is turned is dependent on the translational movement of the axis of shaft 26. The mechanism for rotating drum 103 will now be described. 1

FIGS. 4 and 9 show a shaft 104 extending down to drum 103. This shaft is suitably journalled in a tubular housing 105. At the top end of the shaft there is a sprocket 106. In FIG. 4, within tube arm 7, one may see that there are some direction changing sprockets 107 mounted on a journalled shaft 108 which spans the interior of the tube arm. There is a closed-loop belt 109 running over sprockets 106 and 107 and through the hollow interior of vertical shaft 26 up to another sprocket 110. Sprocket 110 is on the same shaft 111 as is a gear 112. Gear 112 meshes with a gear 113 which is an idler. As can be best seen in FIG. 4, gear 113 also meshes with a gear 1 14 on whose shaft 1 there is also a friction wheel 116 of rubber or the like. Friction wheel 116 bears on a bottom plane surface of fixed reaction plate 117. Since friction wheel 116 is in effect carried on inner carriage l9 coincident with the axis of shaft 26, it is evident that when carriage 19 executes an ellipse thatfriction wheel 116 will also trace out an elliptical path as it rolls on reaction plate 117. Friction wheel 116 as a result of turning, drives the gear train just described as well as belt 109 in which case film drum 103 is caused to rotate. With this arrangement, the amount of film presented is proportional to the size of the ellipse which is generated.

The friction driving system just described is made so that friction wheel 116 may be disengaged from the surface 117 on which it runs. Referring to FIG. 5, one

may see that shaft 111 which carries gear 112 and sprocket 1 10 is journalled for rotation in two stationary upright side members 121 and 122. The shaft 123 which carries gear 113 is also journalled for rotation on the side members 124 and 125. Shaft which carries gear 114 and friction wheel 116 is journalled at its opposite ends in side members 124 and 125. Thus, everything that is carried by upper side members 124 and 125 pivots with these members around the axis of shaft 123 which is journalled in the lower side members 121 and 122. By this means, the friction wheel 1 16 may be swung toward and away from reaction surface 117 while all gears remain meshed.

The upper assembly including the friction wheel is urged upwardly by a torsion solenoid 126, see FIGS. 3 and 5. The torsion solenoid has a disk 127 which takes a partial turn when the solenoid is energized. There is a pin 128 projecting from disk 127 and it bears against the lower edge of upper side member 125. Thus, when the pin is swung through an arc with disk 127, side member 125 rocks upwardly around pivot axis 123 and causes the friction wheel 116 to be engaged. One reason for this is to avoid unnecessary wear of the friction wheel when the tube arm is being swung manually in connection with setting up a subject for taking radiographs. It should be evident that when the two carriages 16 and 19 are in joint motion and friction wheel 116 is tracing an ellipse while it is bearing on stationary reaction surface 1 17, that there are two components of motion one of which induces the roller to roll in the direction of the major axis of the ellipse and the other of which tends to slide the roller in the direction of the minor axis of the ellipse. Hence, the friction wheel is disengaged when it is not being used to drive or rotate the film drum 103.

In summary, a new panoramic dental x-ray unit has been described. Its use involves making a determination of the subject's dental arch size and adjusting an ellipse generating mechanism by remote means to produce a semi-ellipse that closely approximates the dental arch extending from mandibular joint to mandibular joint. The subject's head is then supported on a chin rest so that the arm which carries an x-ray tube casing and film cassette has its center of rotation initially over one of the mandibular joints as depicted in FIG. 2. Correct positioning of the patient may be obtained with some light beam alignment means which have not been shown or discussed because they are conventional. When the subject is set-up, the x-ray source is energized and so is the motor which drives the semi-ellipse generating mechanism and that rotates and translates the tube arm. As the tube arm rotates, its axis of rotation coincides with consecutive points on the dental arch. The x-ray film holder is rotated during this process so that new film is presented as the panoramic image is continually formed. The x-ray beam maintains substantial perpendicularity with the dental arch, thus minimizingdistortion of the image. The distance between the curved plane being radiographed and the film remains constant during the process to minimize magnification and demagnification.

The electric controls for operating the motors that drive the tube arm and set the ellipse size were not shown'because they can be devised by an electric circuit designer. The power supply for the x-ray tube has not been described because it is essentially conventional except that automatic means may be provided to vary the x-ray tube power as required to get satisfactory penetration when the x-ray beam passes from more to less dense regions of the head. For instance, more penetrating power and x-ray intensity may be desired when the subjects spine is in the beam as it is when the incisors are being radiographed. Penetrating power may be changed by changing x-ray tube voltage and intensity may be changed by changing x-ray tube current. Either change may be made coordinately with angular position of the tube supporting arm.

I claim:

1. Apparatus for making a panoramic radiograph of the dental arch of a subject, comprising:

a. a mechanism supporting base positionable over a subjects head,

b. an arm adapted to turn in a horizontal plane on a vertical axis of rotation,

c. an x-ray source and film carrier mounted on said arm on opposite sides, respectively, of the rotational axis whereby said x-ray source and film carrier may orbit the subjects head jointly,

d. a shaft on said vertical axis of rotation, said shaft being fastened at one end to said arm and having its other end extended through an opening in said base,

e. movable means supported on said base and adapted to be moved in a path which simulates the curved shape of the dental arch,

f. said shaft being mounted on said movable means for translation therewith and rotation thereon, the axis of the shaft projecting down through the planes of the dental arch,

g. a mechanism adapted to generate a curve that simulates the shape of the dental arch, said mechanism being coupled with said movable means to cause said movable means and the vertical shaft axis to execute the same movement, and

h. motor driven mechanism carried by said movable means and adapted to turn said shaft synchronously with generation of the curve that simulates the dental arch to maintain said x-ray source and film carrier supporting arm in substantial perpendicularity with said arch as the axis of said shaft moves in a path that is substantially coincident with the dental arch.

2. Apparatus for radiographing' a curved plane in a 7 subject comprising:

a. an overhead support base,

b. a first carriage mounted on said base and means constraining said first carriage to bidirectional movements along one axis of the curved plane,

0. a second carriage mounted on the first carriage and means constraining said second carriage to bidirectional movements along the other axis which is perpendicular to the first axis, said second carriage being translatable with the first carriage,

d. a substantially vertical shaft journalled on said second carriage and extending down through said first carriage,

e. an arm supported by said vertical shaft and adapted to rotate on the axis of said vertical shaft in a substantially horizontal plane above the subject,

f. an x-ray source and a film carrier means mounted on said arm on respectively opposite sides of said vertical axis for jointly orbiting about a space that is to be occupied by the radiographic subject,

g. an electric motor and means coupling said motor with said vertical shaft to swing said horizontal arm about its vertical rotational axis, and

h. a motor driven mechanism adapted to generate a curve that corresponds substantially with the shape of the curved plane, said mechanism being coupled with at least one of said carriages to cause said one carriage and said vertical shaft axis to follow the curved plane in the subject as the arm rotates to orbit the x-ray source and film carrier means around the subject.

3. The invention set forth in claim 2 further including:

a. means that interconnect said vertical shaft and said motor driven mechanism for synchronous operation to maintain said arm in perpendicularity with the curved plane being radiographed as the vertical axis of said shaft follows the curved plane.

4. The invention set forth in claim 2 further including:

a. a rotatable film cassette supporting drum means inside said film carrier means,

b. a wheel driven by friction and journalled for rotation on said second carriage,

c. a fixed planar surface on which said wheel bears and which causes said wheel to be rotated as said carriage follows its curved path, and

d. belt means coupling said wheel and said drum means, whereby said drum means is rotated continuously as the axis of said arm follows its curved path.

5. The invention set forth in claim 2 further including a mechanism for generating a substantially semielliptical curve that corresponds substantially with the dental arch of a subject, said mechanism comprising:

a. a pair of stationary guide members supported on said base, said guide members being arranged perpendicular to each other,

. an ellipse generating arm,

c. a pair of guide member engaging means carried on said arm and each of said means being slidably en gaged with a different one of said guide members, whereby movement of said arm will cause a point thereon to trace an elliptical curve,

. a shaft means at one end of said arm to apply rotational force on the arm,

e. a force transmitting member fastened to said second carriage and journalled on said shaft means,

f. means adapted to rotate said shaft means to cause a point on said arm to move in an elliptical path, said force transmitting member causing said carriage to follow the same elliptical path.

6. The invention set forth in claim 5 including means for varying the length of the axes of the substantial semi-ellipse, said means comprising:

a. means supporting said guide member engaging means adjustably along said ellipse generating arm,

b. lead screw means engaged with the supporting means for the guide engaging means, and

c. means adapted to 'turn said lead screw means for changing the location of said guide engaging means on said ellipse generating arm. i =5 t 9* t 

1. Apparatus for making a panoramic radiograph of the dental arch of a subject, comprising: a. a mechanism supporting base positionable over a subject''s head, b. an arm adapted to turn in a horizontal plane on a vertical axis of rotation, c. an x-ray source and film carrier mounted on said arm on opposite sides, respectively, of the rotational axis whereby said x-ray source and film carrier may orbit the subject''s head jointly, d. a shaft on said vertical axis of rotation, said shaft being fastened at one end to said arm and having its other end extended through an opening in said base, e. movable means supported on said base and adapted to be moved in a path which simulates the curved shape of the dental arch, f. said shaft being mounted on said movable means for translation therewith and rotation thereon, the axis of the shaft projecting down through the planes of the dental arch, g. a mechanism adapted to generate a curve that simulates the shape of the dental arch, said mechanism being coupled with said movable means to cause said movable means and the vertical shaft axis to execute the same movement, and h. motor driven mechanism carried by said movable means and adapted to turn said shaft synchronously with generation of the curve that simulates the dental arch to maintain said x-ray source and film carrier supporting arm in substantial perpendicularity with said arch as the axis of said shaft moves in a path that is substantially coincident with the dental arch.
 2. Apparatus for radiographing a curved plane in a subject comprising: a. an overhead support base, b. a first carriage mounted on said base and means constraining said first carriage to bidirectional mOvements along one axis of the curved plane, c. a second carriage mounted on the first carriage and means constraining said second carriage to bidirectional movements along the other axis which is perpendicular to the first axis, said second carriage being translatable with the first carriage, d. a substantially vertical shaft journalled on said second carriage and extending down through said first carriage, e. an arm supported by said vertical shaft and adapted to rotate on the axis of said vertical shaft in a substantially horizontal plane above the subject, f. an x-ray source and a film carrier means mounted on said arm on respectively opposite sides of said vertical axis for jointly orbiting about a space that is to be occupied by the radiographic subject, g. an electric motor and means coupling said motor with said vertical shaft to swing said horizontal arm about its vertical rotational axis, and h. a motor driven mechanism adapted to generate a curve that corresponds substantially with the shape of the curved plane, said mechanism being coupled with at least one of said carriages to cause said one carriage and said vertical shaft axis to follow the curved plane in the subject as the arm rotates to orbit the x-ray source and film carrier means around the subject.
 3. The invention set forth in claim 2 further including: a. means that interconnect said vertical shaft and said motor driven mechanism for synchronous operation to maintain said arm in perpendicularity with the curved plane being radiographed as the vertical axis of said shaft follows the curved plane.
 4. The invention set forth in claim 2 further including: a. a rotatable film cassette supporting drum means inside said film carrier means, b. a wheel driven by friction and journalled for rotation on said second carriage, c. a fixed planar surface on which said wheel bears and which causes said wheel to be rotated as said carriage follows its curved path, and d. belt means coupling said wheel and said drum means, whereby said drum means is rotated continuously as the axis of said arm follows its curved path.
 5. The invention set forth in claim 2 further including a mechanism for generating a substantially semi-elliptical curve that corresponds substantially with the dental arch of a subject, said mechanism comprising: a. a pair of stationary guide members supported on said base, said guide members being arranged perpendicular to each other, b. an ellipse generating arm, c. a pair of guide member engaging means carried on said arm and each of said means being slidably engaged with a different one of said guide members, whereby movement of said arm will cause a point thereon to trace an elliptical curve, d. a shaft means at one end of said arm to apply rotational force on the arm, e. a force transmitting member fastened to said second carriage and journalled on said shaft means, f. means adapted to rotate said shaft means to cause a point on said arm to move in an elliptical path, said force transmitting member causing said carriage to follow the same elliptical path.
 6. The invention set forth in claim 5 including means for varying the length of the axes of the substantial semi-ellipse, said means comprising: a. means supporting said guide member engaging means adjustably along said ellipse generating arm, b. lead screw means engaged with the supporting means for the guide engaging means, and c. means adapted to turn said lead screw means for changing the location of said guide engaging means on said ellipse generating arm. 